A crop residue spreader for a harvester, such as for example a combine harvester, is known from U.S. Pat. No. 7,331,855. This crop residue spreader makes use of rotating impellers in combination with an airflow. As shown in FIG. 6 of U.S. Pat. No. 7,331,855 the impeller has impeller blades projecting downwards from a rotating impeller disc. This rotating impeller disc forms an upper boundary surface of the rotating impeller which receives an incoming crop residue flow from below. Air fins are secured to the upper side of the rotating impeller disc of the impeller, this means at the opposite side of the rotating disc with respect to the impeller blades. When these air fins are rotated together with the rotating disc and the impeller blades, an airflow is generated is generated by these air fins. The rotating air fins create an airflow that is drawn in through holes in a cover above the rotating disc as shown most clearly in FIG. 5 of U.S. Pat. No. 7,331,855. The rotating air fins then force the airflow over the radial outer edges of the rotating disc. In this way the rotating air fins create an outgoing airflow in the area between the outer radial edge of the impeller disc and a corresponding radial housing that surround the outer radial edge of the impeller disc. This outgoing airflow reduces the risk that crop residue enters, via the cavity between the impeller disc and its radial housing, into the area above the impeller disc. In this way the risk of blockage resulting from clogging or plugging of crop residue in the area in between the upper side of the impeller disc and its corresponding housing is reduced. The problem with this particular type of airflow providing a cleaning function is that the outgoing airflow generally forms a sort of downwards, radial air curtain around the rotating impeller disc and thus also around the impeller blades. This downwards, radial air curtain disturbs the outgoing crop residue flow generated by the impellers. In this way this downwards, radial air curtain negatively affects the maximum width over which the crop residue flow can be spread by the rotating impeller blades. This is in particular the case for crop residue with a relatively small weight and/or small particle size such as for example chaff. The crop residue flow confining function of such an air curtain has for example been documented in EP2340703.
Further embodiments of crop residue spreaders are for example also known from U.S. Pat. No. 4,917,652, EP0631717 and DE19750393. These documents disclose a combine harvester with a crop residue spreader for spreading a grain-chaff mixture. This crop residue spreader also comprises oppositely rotatable impellers which each comprise an impeller disc to which impeller blades are mounted. The impellers of the crop residue spreader are also provided with a cup-shaped radial housing which partially surrounds the radial outer edges of the rotating impeller discs and comprises an outlet opening for ejecting an outgoing crop residue flow via an outlet nozzle. The incoming crop residue flow is generally received from above the impellers. The rotating impeller blades mounted on top of the impeller discs subsequently cooperate with the radial cup-shaped housing to propel the crop residue flow through the outlet nozzle.
According to some embodiments, such as for example FIGS. 1-3 of U.S. Pat. No. 4,917,652, FIGS. 1-4 of EP0631717 or the embodiments of DE19750393, an incoming suction airflow is generated by means of the impeller blades themselves in order to enable a more efficient intake of lighter crop residue components such as chaff into the crop residue spreader. However in order to generate such an incoming suction airflow by means of the impeller blades themselves, the impellers need to be provided with an inlet opening for the incoming crop residue flow which has a radius that is smaller than the radius of the rotating impellers. In this way the crop residue flow is not directly impacted by the most radially outward part of the impeller blades, which has the highest absolute velocity, thereby limiting the maximum distance over which the crop residue can be spread. Additionally a part of the generated airflow escapes, downwards, in between the impeller disc and the cup-shaped radial housing. This reduces the part of the generated airflow that is propelled through the outlet opening to the outlet nozzle, thereby also limiting the maximum distance over which the crop residue can be spread. Additionally this also requires the crop residue flow to be constricted to this reduced inlet opening towards the impeller blades, thereby increasing the risk of spillage or leading to converging funnel like elements that disturb the incoming crop residue flow and increase the risk of blockage. Still further the incoming crop residue flow and the incoming suction airflow are received through the same inlet opening. It is clear that uncontrolled variations in the incoming crop residue flow will inevitably also cause uncontrolled variations in the incoming suction airflow. The same holds for the uncontrolled variations in the crop residue flow in the area of the impeller blades which will inevitably cause uncontrolled variations in the generated airflow as the impeller blades are used as airflow generating elements. Such uncontrolled variations in the generated airflow, will clearly also result in uncontrolled variations in the maximum distance over which the crop residue can be spread. Additionally when the impeller blades are functioning both as an element for propelling the crop residue flow and as an element for generating an airflow, its arrangement and/or shape cannot be optimized for both functions. For example the optimal number of these elements, their optimal angle with respect to the radial direction, their optimal shape, etc. differs considerably for both respective functions. In this way the impeller cannot be designed to both generate an optimal airflow and optimally propel the crop residue, which limits the maximum distance over which the crop residue flow can be spread.
According to some alternative embodiments, such as for example FIGS. 2, 5 and 6 of U.S. Pat. No. 4,917,652; FIGS. 5, 7 and 8 of EP0631717, the impeller comprises impeller blades projecting from a first axial side of the impeller disc. For the referenced embodiments above this means that the impeller blades project upwards from the impeller disc, and thus project from the axial side of the impeller disc that faces the incoming crop residue flow. Further the impeller also comprises air vanes projecting from a second axial side of the impeller disc. For the referenced embodiments above this means that the air vanes project downwards from the impeller disc, and thus project from the axial side of the impeller disc that faces away from the incoming crop residue flow. When the impeller disc is rotatably driven the air vanes cooperate with an air inlet opening in the cup-shaped radial housing. This air inlet opening is provided in the cup-shaped radial housing at a side facing the air vanes. For the embodiments referenced above this thus means that the air inlet opening is provided below impeller disc in the bottom of the cup-shaped radial housing. The air vanes, when rotated, in this way create an incoming suction airflow through this air inlet opening. The air vanes propel this airflow through a radial outlet opening in the radial housing into an outlet nozzle. At the same time, at the other axial side of the impeller disc, the rotatably driven impeller blades receive the incoming crop residue flow through a crop residue inlet opening in the cup shaped radial housing. This crop residue inlet opening is provided at the side facing the impeller blades. This means, for the embodiments referenced above, that the crop residue inlet opening is provided above the impeller disc at the top of the cup-shaped radial housing. The crop residue received though the crop residue inlet opening is impacted by the rotatably driven impeller blades and propelled through the radial outlet opening in the radial housing into the outlet nozzle. In the outlet nozzle the outgoing crop residue flow is assisted by the outgoing airflow generated by the air vanes in order to increase the maximum distance over which the outgoing crop residue flow can be spread. This allows for embodiments in which the setup of the impeller blades and the air vanes can be differentiated in order to optimize both respective functions, for example by differentiating their number, their angle with respect to the radial direction, their shape, etc. However, also these embodiments present some particular disadvantages.
There is the risk that at least a part of the incoming suction airflow escapes axially in between the radial edge impeller and the radial housing in the direction of the incoming crop residue flow. This reduces the part of the generated airflow that is propelled through the outlet opening to the outlet nozzle, thereby also limiting the maximum distance over which the crop residue can be spread. Additionally, similar as explained above, this escaping airflow creates an upwards air curtain that disturbs the incoming crop residue flow leading to the risk of spillage at the crop residue inlet opening, even when the crop residue inlet opening has a radius that is larger than the radius of the rotating impellers. It is further also clear that the height of the outlet opening to the outlet nozzle, this means the distance of the outlet opening along the axial direction of the rotation axis of the impeller needs to be divided respectively between the height of the impeller blades and the height of the air vanes. It is thus clear that for a given height of the outlet opening the height of the impeller blades must be reduced with the height of the air vanes, and vice versa. This means that for a given height of the outlet opening the area of the impeller blades with which the crop residue flow is impacted will be reduced, in function of the area claimed by the air vanes for generating a suitable airflow, and vice versa. This leads to a design compromise in which both the acceleration of the crop residue flow by the impeller blades, as well as the volume and flow rate of the airflow generated by the air vanes are suboptimal, thus limiting the maximum distance over which the crop residue flow can be spread. Additionally the crop residue flow and the airflow are provided to the outlet opening in a layered way, as they are generated at different axial sides of the impeller disc. When reaching the outlet opening the crop residue flow generated by the impeller blades is thus still separated by the impeller disc from the airflow generated by the air vanes along the axial direction. This thus means that, before the generated airflow can interact with the crop residue flow, the airflow and/or the crop residue flow must first expand in the outlet nozzle along the axial direction of the impeller. It is clear that such an expansion reduces the flow rate of both the airflow and the crop residue flow and causes turbulences which still further reduce the flow rate. Additionally, it is clear that, it is necessary to provide sufficiently long and confined outlet nozzles in order to ensure sufficient mixing of the expanding airflow and the crop residue flow. Such ejection nozzles form a constriction which increases the risk of clogging or blockage. Additionally such ejection nozzles constrict the width of the outgoing crop residue flow to a rather narrow beam. This often leads to the need to provide for an oscillating movement of at least the radial position of the downstream end of these ejection nozzles in order to more uniformly distribute the crop residue flow across a wider area behind the harvester, thereby leading to a complex construction which is complex to control in function of varying harvesting or operating conditions.
Therefor there still exists a need for an improved crop residue spreader that is able to robustly and efficiently cope with further increases with respect to the desired maximum spreading width of the outgoing crop residue flow. Such a need is for example relevant for crop residue spreaders of a harvester, such as for example a combine harvester, in which there is made use of headers with an increasing width in the context of increasing harvesting capacities. This leads to an increasing difficulty to spread the crop residue flow in an efficient and robust way up till the desired maximum width. This desired maximum width for example being determined by width of the header of the combine harvester.